This invention is directed to an improved gas sensor for use in sensing biologically important gases in vivo. The gas sensor includes an emulsoid of an aqueous dye containing buffer solution in a gas permeable cross-linked polymer.
In many situations, it is extremely important to determine the partial pressure of a gas in a fluid. One such situation is the determination of blood gas in warm blooded animals as for instance the concentration of blood gas in a human patient's blood during the performance of medical procedure on that patient.
Lubbers et al, U.S. Pat. Res. 31,879, describes an apparatus for making such a determination. The apparatus of Lubbers et al utilizes light of a particular frequency band width which is directed onto a sample cell (which Lubbers refers to as an optode). A biological fluid of interest is positioned in association with the cell for the determination of the partial pressure of the gas therein.
Heitzmann, U.S. Pat. No. 4,557,900, is also directed to gas sensing devices. In Heitzmann, dye particles are taken up in a hydrophilic fluid and then are absorded or absorbed on carrier beads of particles. These beads or particles are then taken up in a matrix of a hydrophobic material. Thus for instance Heitzmann forms a solution of beta-methylum-belliferone in sodium bicarbonate and absorbs this solution into the voids of polyacrylamide particles. These particles are of the order of 35 microns in size. The particles are then incorporated into a polymerized disk of polymeric material. The disk, which may be of a size of approximately 100 microns thick by 3 mm in diameter, is associated with a fiber optic bundle in a cassette. The cassette is then utilized for sensing blood gases.
The devices of both Lubbers et al and Heitzmann incorporated very useful blood gas measurement techniques. Both Lubbers et al and Heitzmann take advantage of fluorescent or absorption properties of a dye upon interaction either directly or indirectly with the gas of interest. The interaction of the dye with the gas is then measured spectrophotometrically. This technique has many basic merits and, in fact, similar techniques are utilized for this invention. In both Lubbers et al and Heitzmann the before mentioned optical indicator dye is used to indirectly measure carbon dioxide through an acid base interaction of the gas and the dye.